Optical touch pads and touch screens may be seen in e.g. U.S. Pat. No. 4,346,376, U.S. Pat. No. 4,484,179, U.S. Pat. No. 4,688,933, U.S. Pat. No. 5,525,764, U.S. Pat. No. 5,945,981, U.S. Pat. No. 6,492,633, U.S. Pat. No. 6,664,952, U.S. Pat. No. 6,972,753, US2003/0048257, US2004/0201579, US2004/0252091, US2006/0114237, US2007/0024598, US2007/0075648, EP0600576 and EP1126236, as well as in WO2005/026938 and WO2007/112742.
The prior art also comprises U.S. Pat. No. 5,775,792, U.S. Pat. No. 6,122,394, U.S. Pat. No. 6,648,485, and US2003/0052257.